A large number of regulation and control systems are used today in automotive engineering. With many of these systems, it is necessary to sense various physical magnitudes by means of a sensor system, and convey them to the corresponding control device. An example that may be mentioned here is sensing of the oil temperature in the transmission, in the context of the transmission control system.
FIG. 5 shows a prior art circuit arrangement for a transmission control system in which the signal generated by the temperature sensor, which in this case represents the temperature of the oil in the transmission, is transmitted by means of two signal lines to the control device. To this end, there is mounted in the transmission (107) a sensor means (201) which is connected, via a first signal line (301a) and a second signal line (301b), to an input circuit (202') contained in a control device (306). Signal UTol' generated by the sensor means is transmitted by means of the first signal line. The sensor means is connected to the ground A/D-GND of the control device via the second signal line. The input circuit consists of a component (RV1) which is used as a protective resistor, and of a filter which is made up of components RF1 and CF. The input circuit is connected via a first signal line (305a) and a second signal line (305b) to a microcontroller (204'). Signal UTol* is transmitted to the microcontroller by means of the first signal line. The second signal line connects the microcontroller to ground A/D-GND.
Since the transmission and the control device are arranged physically apart from one another in the vehicle, the signal lines must be routed outside the control device. As a result, interference signals can in some circumstances be coupled onto the two signal lines.
An arrangement for blanking out interference signals on signal lines is described in German Patent No. 42 22 475. In a first exemplifying embodiment, an arrangement is presented that can be used in the transmission of analog signals. In this context, the original signal is transmitted on a first signal line, and the time derivative of the original signal is transmitted on a second signal line. At the receiving end, the derived signal transmitted on the second signal line is integrated by means of an integrator. An analog AND instruction is applied to this integration signal and to the original signal transmitted on the first signal line. The interference signals coupled onto the transmission link are thereby eliminated. In a second exemplifying embodiment, an arrangement is presented which can be used in the transmission of digital signals. To this end, the original signal is transmitted on a first signal line, and the inverted original signal is transmitted on a second signal line. At the receiving end, the two signals are each digitized by means of a digitizing stage. The coupled-in interference is thus also present in digitized form. The digitized signal of the inverted original signal transmitted on the second signal line is inverted again at the receiving end. A logical AND instruction is applied to this signal and to the digitized signal of the original signal transmitted on the first signal line. The interference signals coupled onto the transmission link are thereby eliminated.
The arrangements in the first and the second exemplifying embodiment have the disadvantage that they must use not only very precisely operating components, but also components that are very well tuned to one another. If this is not the case, a certain proportion of the interference signal may still be present in the usable signal.
U.S. Pat. No. 3,906,384 describes an arrangement with which interference signals, which are overlaid on the usable signal during processing thereof in processing components, are eliminated. In an exemplifying embodiment, an arrangement is presented in which the usable signal is fed on the one hand unchanged to first processing components, and on the other hand in inverted form to second processing components. With the prerequisite that the first and the second processing components are identical, the same interference is then superimposed on the signals present after processing by the processing components. The signals present after processing by the processing components are both fed to a subtracter. The interference caused by the processing components is thereby eliminated.
This arrangement has, however, the following disadvantages: On the one hand, implementation is complex because of the double processing components required. On the other hand, the processing components must be very well matched to one another, since the interference signals can be eliminated only if they are generated identically. In addition, the signal level of the usable signal is doubled by this arrangement.
It is the object of the present invention to improve the elimination of interference signals coupled onto the signal lines during the transmission of signals.